1. Field of the Invention
The present invention relates to a cryopump.
2. Description of the Related Art
A cryopump is a vacuum pump that captures and pumps gas molecules by condensing or adsorbing molecules on a cryopanel cooled to an extremely low temperature. The cryopumps is generally used to achieve a clean vacuum environment required in a semiconductor circuit manufacturing process or the like.
For example, Japanese Patent Application Publication No. Hei 3-23386 discloses a cryopump in which a baffle is provided in an opening portion of a radiation heat shield panel surrounding a second panel. The baffle is structured by a first baffle and a second baffle. Each of the first and the second baffles is formed into the same structure with each other by louvers that incline upwards/downwards. Each louver is fixed to the opening portion of the shield panel such that the outer circumferential portion thereof faces the adjacent louver in the upward-downward direction.
Because the aforementioned cryopump is provided such that the louvers face each other in the upward-downward direction in each of the first and the second baffles, each of the first and the second baffles optically occludes the inside of the cryopump. That is, when viewing from outside the first baffle in the central axis direction of the cryopump, the inside of the pump cannot be seen through the first baffle. The same is true with respect to the second baffle. According to this structure, entry of radiation heat from outside can be suppressed; however, gas molecules to be pumped by the second panel are difficult to pass through the baffle. Flow resistance of a gas is further increased due to installation of the second baffle in addition to the first baffle, causing an pumping speed of the cryopump to be small in addition to heat input.